An electric heater uses natural convection to heat water \(\left( {K = 0.6\frac{w}{{mK}}} \right)\) using a rod of 1 cm diameter and 0.65 m length at 110 volt. The heater surface temperature is 120°C, and water temperature is 35°C. If Nusselt number based on diameter is 6, current passing through the heater is